This invention relates to marine vessel drive units of the known kind in which an inboard engine is coupled to the propeller by an engine shaft extending to and through (or over) the vessel transom, and having a power leg which extends generally vertically downwards to transmit drive to the propeller which is usually carried on a shaft parallel to the engine shaft, although it will be appreciated that the engine shaft could be horizontal or inclined and the propeller axis determined by the trim of the vessel and other considerations.
There is a requirement or desirability for several distinct movements of the propeller shaft, namely the capability for upward pivoting so that in the event of the power leg hitting an underwater obstacle it can kick up to minimise risk of damage to the power leg, and for like movements to smaller degree to trim the propeller to the most favourable angle for drive.
For beaching of vessels it is also desirable to have such capability, although it is sometimes preferred to swing the power leg laterally instead of rearwardly and upwardly, and like movement capability is also useful for inspection, maintenance and the like.
For steering purposes it is usually preferred to turn the propeller shaft about the power leg axis or like, thus avoiding the need for a separate rudder.
In order to provide some or all of these movements many different designs have been proposed, but in order to maintain the drive transmission (and also steering connections) it has often been necessary to provide several universal joints in the drive shafts and also provide complex sets of gimbals, swivels and the like.